There is, of course, a need for alloys for use at temperatures over 650.degree. C. which must have high tensile, yield and creep-rupture strengths at elevated temperatures. One such alloy is described in U.S. Pat. No. 2,994,605; and while very broad ranges of composition are given in that patent, the only specific examples given have the following range of composition: about 50 to 70% nickel, about 14% chromium, about 2% niobium and/or tantalum, about 2.75 to 3.5% molybdenum and/or tungsten, less than 0.1% titanium, about 1% aluminum, about 0.35% manganese, about 0.5 to 0.75% silicon, about 0.03% carbon and the remainder iron. Such an alloy is described as having an ultimate tensile strength of 115,000 p.s.i. and a 0.2% yield strength of 46,750 p.s.i. at room temperature.